Unfortunately kava wont convert that way. Depending on how dry it is, how dense it is, and how much resin is contains will all cause the measurements to be different. You're going from volume to weight. A pound of feathers weighs as much as a pound of bricks, but a pound of bricks takes up way less volume because it is so compact. Without knowing the cubic density you wouldn't be able to accurately measure how much a certain amount would weigh
However! I would supposed kava had similar (definitely not exact) properties dry as dried wheat flour. If this is correct then 168 teaspoons would equal a pound. Again, only a really rough estimate at this point. I'll measure a teaspoon when I get home.
